GERDA will be a new underground experiment at the Laboratori Nazionali del Gran Sasso (LNGS) with the aim to study neutrinoless double beta (0νββ) decay of 76Ge at background levels (<10−3 cts/(keV × kg × yr) at Qββ = 2039 keV) which are more than two orders of magnitude lower than in existing 0νββ experiments. Bare Ge-diodes, enriched to 86% in 76Ge, are operated in a 2 m thick shield of liquid nitrogen or argon complemented by a water shield of 3 m thickness to reduce the external backgrounds.